The Federal Aviation Administration (FAA) requires that commercial airports have a standard runway safety area (RSA) where possible. The RSA is the area surrounding the runway specially prepared or suitable for reducing the risk of damage to airplanes in the event of an undershoot, overshoot, or excursion from the runway. At most commercial airports, the standard RSA is 500 feet wide and extends 1,000 feet beyond each end of the runway. Since many airports were built before the 1,000-foot extension requirement was mandated over 20 years ago, the area beyond the end of the runway is where many airports cannot achieve the full standard runway safety area.
Recognizing the need for increased airport safety within the practical constraints of the land available around many airports, research programs were designed to develop technologies to safely stop an aircraft during an overrun event using less than the standard 1000 foot runway safety area. The culmination of the research in soft ground arresting systems has been the implementation of Engineered Material Arresting Systems (EMAS) at numerous airports. As of February 2014, at least 74 EMAS had been installed at 47 airports throughout the U.S.
EMAS are used at airports where the 1000 foot RSA's cannot be met due to the presence of bodies of water, local development, or other obstacles. EMAS are designed and installed under the guidance of FAA Advisory Circular 150/5220-22B (incorporated herein by reference in its entirety).
A number of guidelines and design standards for EMAS outlined in AC 150/5220-22B are summarized below. Although the summaries below use the term “must”, and the FAA recommends that the guidelines for EMAS in this circular be followed by all airport operators, these guidelines are not strictly mandatory unless the EMAS is funded by federal grant assistance programs or installed at an airport which is certificated under 14 C.F.R. § 139 (“Airport Certification”).
In brief, an EMAS is designed to stop an overrunning aircraft by exerting predictable deceleration forces on its landing gear during the overrun event as the EMAS material deforms. The EMAS should be designed to minimize the potential for structural damage to aircraft as such damage could result in injuries to passengers and/or affect the predictability of deceleration forces of the EMAS. The EMAS should be designed with the expectation of a 20-year service life.
An EMAS must be located beyond the end of the runway and be centered on the extended runway centerline. The EMAS will usually begin at some setback distance from the end of the runway to avoid damage due to jet blast and undershoots, and this distance will vary based upon the available area and local conditions.
U.S. Federal Aviation Administration guidelines provide that an EMAS should decelerate the design aircraft (the airplane type that regularly uses a particular runway and that imposes the greatest demand on the EMAS) which leaves the runway and enters the EMAS at a speed of 70 knots. If there is insufficient space for a standard EMAS bed, a non-standard EMAS should be designed for a 40-knot minimum aircraft speed. An EMAS that cannot provide at least this minimum performance is not considered a cost-effective safety enhancement.
The EMAS must be a passive system which does not require external means to initiate or trigger the operation of the EMAS to arrest an aircraft's movement. The minimum width of the EMAS is to be the width of the runway, and the width is to be based on the standard runway width for the applicable aircraft design group. The EMAS must be constructed on a paved base which should perform satisfactorily under all local weather, temperature, and soil conditions. The EMAS also should not allow water to accumulate on the surface of the bed, runway, or RSA, and allow snow and ice to be removed.
In accordance with AC 150/5220-22B, an EMAS design must be supported by a validated design method that can predict the performance of the system using the aircraft that imposes the greatest demand upon the EMAS, which is usually the largest/heaviest aircraft which uses the runway. The design must be derived from field or laboratory tests which are based on the passage of an actual aircraft or equivalent single wheel through a test bed. The model must consider multiple aircraft parameters such as (but not limited to) aircraft gear loads, gear configuration, tire contact pressure, and aircraft speeds.
FAA Order No. 5200.9 (incorporated herein by reference in its entirety) provides airport operators with additional guidance regarding (a) RSA improvement alternatives that use EMAS systems, and (b) determining the maximum financially feasible cost for RSA improvements, whether they involve EMAS or not.
Overrun events can be caused by many factors, and can occur during taxiing on the ground, during an aborted or rejected takeoff when the aircraft does not leave the ground, or during landing when the aircraft cannot stop before the end of the runway. There are several general assumptions which are used for all EMAS designs, as summarized below:                A. an aircraft is still attempting to stop as the runway is exited;        B. there is minimal or no structural damage to the landing gear; and        C. there is no aircraft braking or use of reverse thrust/reverse pitch once an aircraft enters the EMAS.        
In order to obtain the greatest arresting effects from an EMAS, the pilot of the aircraft usually aims for the centerline of the extended runway and, once stopped in the EMAS area, the aircraft is to remain stationary and to await further assistance from airport ground staff.
Within the United States, most of the EMAS have been installed by the Engineered Arresting Systems Corporation (ESCO) of Logan Township, N.J., as ESCO had been the only supplier qualified to design and install EMAS systems. In 2014, an arrestor system utilizing foam glass topped by a layer of concrete and a polymer topcoat was installed at Midway Airport (Chicago) by Runway Safe (Austin, Tex.). In September 2015, Runway Safe announced that they would install five additional EMAS systems at Midway and O'Hare Airports in Chicago. Specific details regarding the structure and composition of this system were not provided.
Current EMAS system arrestor beds in the U.S. today are required to observe the following condition: “Materials must meet a force vs deformation profile within limits having been shown to assure uniform crushing characteristics, and therefore predictable response to an aircraft entering the arresting system.”
The materials comprising the EMAS must satisfy a number of requirements which can be quickly summarized as being non-flammable and able to resist the elements. Finding a material that can do both suggests looking at natural inorganic materials, materials used in building and construction, and hybrid materials where each component addresses one or more of the FAA requirements.
While there are certain polymeric materials which satisfy FAA flammability and environmental resistance requirements, all of these materials are very expensive and structurally reinforced to the point that they would make very poor runway arrestor materials. Consequently, most research has focused on inorganic materials and composites rather than organic-based polymeric materials.
U.S. Pat. No. 8,579,542 to Narmo (assigned to Norsk Glassgjenvinning AS, Norway) discloses a vehicle arresting system for decelerating vehicles. The vehicle arresting system includes a bed filled with foamed glass aggregate, and a top lid covering the upper surface of the bed. The foamed glass aggregate is in the form of glass which is melted, aerated, solidified, and then crushed to obtain rough broken particles with sizes ranging from 0.25 cm to 15 cm. Narmo does not disclose aggregates comprising smooth rounded particles, or particles having a narrow controlled size range.
US 2013/0020437 to Valentini et al. (assigned to Engineered Arresting Systems Corporation, Aston, Pa.) discloses packaging and covers for maintaining integrity of a vehicle arresting bed formed of aggregates such as those disclosed by Narmo. The beds are covered in whole or part with a geotextile in the form of mesh or a net, or are bagged or boxed and covered with asphalt. In certain embodiments, loose aggregates are mixed with adhesives or binders to form bricks or other integrated units. Valentini does not disclose smooth rounded aggregates. Valentini also does not disclose installing vehicle beds in containers with lids which support the weight of a light object such as a person.
U.S. Pat. Nos. 6,685,387; 6,971,817; 7,261,490; and 7,597,502 to Allen at al. (assigned to Engineered Arresting Systems Corporation, Aston, Pa.) are directed to jet blast resistant vehicle arresting blocks, beds, and methods. The arresting beds are formed of a block of a compressible material such as cellular concrete, and an intermediate material such as a foam layer is positioned over the compressible material. A frangible top covering the block is disclosed to provide a damage-resistant surface. Allen does not disclose smooth rounded glass aggregates as an arresting medium.
U.S. Pat. No. 5,885,025 (assigned to Datron Inc., Garland, Tex.) and U.S. Pat. No. 6,726,400 (assigned to Engineered Arresting Systems Corporation, Aston, Pa.), both to Angley et al., disclose vehicle arresting beds formed from a large number of blocks of cellular concrete having predetermined compressive gradient strength. The beds have an entry region formed of blocks having a first compressive gradient strength, and a second region formed of blocks having a greater compressive gradient strength than that of the first region. Angley does not disclose arresting beds of aggregates formed of smooth rounded glass particles as an arresting medium.
There is a continuous desire for new kinds of systems which can be used to arrest movement of a moving aircraft and which are cost-competitive with current EMAS systems. For example, there is a need for novel arrestor systems into which aircraft tires can sink and which can dissipate large amounts of kinetic energy while simultaneously satisfying the need for resistance to the elements and jet blast.